1. Field of the Invention
The present invention relates to a magnetic head for perpendicular magnetic recording that is used for writing data on a recording medium by means of a perpendicular magnetic recording system, and more specifically, to a magnetic head for perpendicular magnetic recording that has a shield provided around a main pole.
2. Description of Related Art
The recording systems of magnetic read/write apparatuses include a longitudinal magnetic recording system wherein signals are magnetized in a direction along the plane of the recording medium (the longitudinal direction) and a perpendicular magnetic recording system wherein signals are magnetized in a direction perpendicular to the plane of the recording medium. It is known that the perpendicular magnetic recording system is harder to be affected by thermal fluctuation of the recording medium and capable of providing higher linear recording density, compared with the longitudinal magnetic recording system.
Magnetic heads for perpendicular magnetic recording typically have, like those for longitudinal magnetic recording, a structure where a read head having a magnetoresistive element (hereinafter, also referred to as MR element) for reading and a write head having an induction-type electromagnetic transducer for writing are stacked on a substrate. The write head includes a main pole that produces a magnetic field in a direction perpendicular to the plane of the recording medium. The main pole includes, for example, a track width defining portion having an end located in a medium facing surface that faces the recording medium, and a wide portion that is connected to the other end of the track width defining portion and is greater in width than the track width defining portion. The track width defining portion has a generally constant width. To achieve higher recording density, it is required that the write heads of the perpendicular magnetic recording system be smaller in track width and improved in write characteristics such as an overwrite property which is a parameter indicating an overwriting capability.
A magnetic head for use in a magnetic disk drive such as a hard disk drive is typically provided in a slider. The slider has the medium facing surface mentioned above. The medium facing surface has an air inflow end (a leading end) and an air outflow end (a trailing end). The slider is designed to slightly fly over the surface of the recording medium by means of an airflow that comes from the air inflow end into the space between the medium facing surface and the recording medium. The magnetic head is typically disposed near the air outflow end of the medium facing surface of the slider. In a magnetic disk drive, positioning of the magnetic head is performed by a rotary actuator, for example. In this case, the magnetic head moves over the recording medium along a circular orbit about the center of rotation of the rotary actuator. In such a magnetic disk drive, a tilt of the magnetic head with respect to the tangent of the circular track, which is called a skew, occurs according to the position of the magnetic head across the tracks.
In particular, in a magnetic disk drive of the perpendicular magnetic recording system which is higher in capability of writing on a recording medium than the longitudinal magnetic recording system, the skew mentioned above can cause the phenomenon that signals already written on one or more tracks that are adjacent to a track targeted for writing are erased or attenuated during writing of a signal on the track targeted for writing (such a phenomenon will hereinafter be referred to as adjacent track erase). To increase the recording density, it is required to prevent the occurrence of adjacent track erase.
A known technique for preventing adjacent track erase resulting from the skew is to configure the main pole so that its end face located in the medium facing surface decreases in width with increasing proximity to the top surface of the substrate, as disclosed in U.S. Patent Application Publication No. 2007/0177301 A1 and U.S. Pat. No. 6,954,340 B2, for example.
Another effective technique for preventing adjacent track erase resulting from the skew is to provide two side shields on opposite sides of the main pole in the track width direction, as disclosed in U.S. Patent Application Publication No. 2007/0177301 A1. It is also effective to provide a shield having an end face that is located in the medium facing surface and wraps around the end face of the main pole (such a shield will hereinafter be referred to as a wrap-around shield), as disclosed in U.S. Pat. No. 6,954,340 B2 and U.S. Patent Application Publication No. 2005/0128637 A1. The wrap-around shield includes a bottom shield that is located on the air-inflow-end side relative to the main pole, a top shield that is located on the air-outflow-end side relative to the main pole, and two side shields that are located on opposite sides of the main pole in the track width direction. These techniques allow capturing a magnetic flux that is produced from the end face of the main pole and expands in the track width direction. This makes it possible to prevent the occurrence of adjacent track erase.
FIG. 14 and FIG. 15 of U.S. Pat. No. 6,954,340 B2 show a magnetic head with a write gap disposed on a first return pole which also serves as the aforementioned bottom shield, and the main pole disposed on the write gap. A part of the coil is arranged to pass through the space defined by the first return pole and the main pole. Such a structure is disadvantageous in that it is difficult to bring the first return pole and the main pole into sufficiently close proximity to each other, and it is thus difficult for the first return pole to satisfactorily function as a shield.
In the magnetic head shown in FIG. 15 of U.S. Pat. No. 6,954,340 B2, the distance between two side parts of the main pole in the medium facing surface decreases with increasing proximity to the top surface of the substrate, whereas the distance between two sidewalls of the two side shields that are opposed to each other with the main pole therebetween is constant regardless of the distance from the top surface of the substrate. Consequently, in the medium facing surface of this magnetic head, the distance between a side part of the main pole and the opposing sidewall of the side shield increases with increasing proximity to the top surface of the substrate. In this structure, in the medium facing surface, the side part of the main pole and the sidewall of the side shield cannot be close to each other across the entire area where they are opposed to each other. Thus, this structure is disadvantageous in that it is difficult for the two side shields to satisfactorily capture a magnetic flux that is produced from the end face of the main pole and expands in the track width direction.
U.S. Patent Application Publication No. 2005/0128637 A1 shows in FIG. 8 a magnetic head including a bottom shorting shield connected to a first return pole and a top shorting shield connected to a second return pole. The lengths of the two shorting shields in the direction perpendicular to the medium facing surface are much smaller than the lengths of the two return poles in the direction perpendicular to the medium facing surface, and are constant regardless of the distance from the main pole. Accordingly, this magnetic head is disadvantageous in that it is difficult for the two shorting shields to direct much magnetic flux to the two return poles.